A leaked Red Cross report on CIA mistreatment of detainees is devastating, providing enough evidence to open a criminal investigation, say human rights organisations.
Published excerpts from the internal report by the Swiss-run International Committee of the Red Cross (ICRC), contain first-person accounts detailing CIA interrogation techniques of al-Qaeda suspects held in secret prisons overseas.
The report says these techniques "constituted torture".
The ICRC report was obtained by Mark Danner, a US writer and professor at the University of California at Berkeley, and appears in the April 9 issue of the New York Review of Books in an article entitled "US Torture: Voices from the Black Sites".
"This is just devastating for the Bush administration. It's the nail in the coffin," Reed Brody, European spokesman for Human Rights Watch, told swissinfo. "It's significant, as it really confirms all that we have heard from sources; now we are getting it from the mouths of detainees."
The inescapable conclusion is that US officials engaged in criminal activities in violation of international and American law, said Brody, who is the author of numerous books on the abuse of detainees.
The report gives fresh ammunition to demands that Bush administration officials be prosecuted for their conduct, say human rights activists.
"There is certainly enough evidence for a full criminal investigation into what has gone on in the US secret detention programme and the wider detention programme since 9/11," said Rob Freer from Amnesty International.
"When the ICRC uses the word torture it doesn't do so lightly. Torture is a crime under international law and when there are credible allegations of torture the US is under obligation to investigate and bring to justice perpetrators."
The ICRC findings were based on its access to the CIA's 14 "high-value" detainees who were held in secret CIA prisons. They were interviewed after being transferred to Guantanamo Bay in 2006. The ICRC has an international role in monitoring standards for prisoners and trying to ensure compliance by governments with the Geneva Conventions.
According to the 2007 report, as quoted by Danner, the prisoners separately and consistently described long-term solitary confinement, waterboarding - which simulates drowning - prolonged stress positions, forced prolonged nudity, beatings, denial of solid food and other forms of abuse.
"The allegations of ill-treatment of the detainees indicate that, in many cases, the ill-treatment to which they were subjected while held in the CIA programme, either singly or in combination, constituted torture. In addition, many other elements of the ill-treatment, either singly or in combination, constituted cruel, inhuman or degrading treatment," stated the report, according to Danner.
ICRC officials did not dispute the report's authenticity, but a spokesman at the agency's headquarters in Geneva regretted that the document was made public. The CIA declined to comment.
In 2006 former US President George W Bush admitted the use of coercive interrogation tactics on senior al-Qaeda captives detained by the CIA following the September 11 attacks. Bush certified in 2007 that the CIA's interrogation programme complied with the Geneva Conventions.
The Obama administration has ordered the secret prisons - so-called black sites - closed and has restricted the CIA to using only those interrogation methods approved for use by the US military until a complete review of the programme is conducted.
There is speculation the ICRC report may have been leaked by officials in the current administration amid political debate over detention policies and accountability.
Some Democrats in Congress have called for a truth commission to investigate a range of alleged abuses by the former administration as part of the "war on terror", including CIA interrogations at secret sites and wiretapping. Republicans have called the move a "witch hunt".
Obama has offered a cool reception to truth commissions but has not ruled out possible prosecutions, saying no one should be above the law.
However, the president said last month that he was "more interested in looking forward than I am in looking backwards".
"I understand the political dilemma facing the new administration that wants to look forward with a broad agenda beyond human rights," said Brody.
"But for the US to regain credibility the investigation and prosecution of these crimes would be a very important step to show the world that not only do we think these acts were wrong but we are dedicated to punishing officials who engage in such un-American activities."
swissinfo, Simon Bradley in Geneva
Claims that the CIA held al-Qaeda suspects in Eastern Europe, Thailand and Afghanistan were first reported in the Washington Post on November 2, 2005.
According to the paper, centres, so-called "black sites", were established following the September 11 attacks in 2001. Egypt, Jordan, Morocco and other countries were also destinations for captives, it claimed.
Swiss senator Dick Marty was appointed by the Council of Europe in November 2005 to investigate claims that the CIA had set up such secret prisons in Eastern Europe.
In his initial report, published in June 2006, Marty concluded that 14 European countries had colluded with the US in a "spider's web" of human rights abuses. Marty said other countries, including Switzerland, had been involved actively or passively in the detention or transfer of unknown persons.
In September 2006 President Bush admitted for the first time that the CIA had been holding suspected terrorists in secret prisons, and announced that 14 detainees - including the alleged mastermind of the September 11 attacks, Khalid Sheikh Mohammed - had been transferred to Guantanamo Bay. However, Bush did not say where the prisons were located.
In December 2007 Bush rejected claims his administration used torture and defended the CIA's methods.
Barack Obama ordered the closing within a year of the Guantanamo Bay military prison in Cuba and of "black sites", and has restricted the CIA to using only those interrogation methods approved for use by the US military until a complete review of the programme is conducted.